As a technique of manufacturing a silicon epitaxial wafer (to be abbreviated as “epitaxial wafer” in some cases hereinafter), there is a vapor phase growth method which grows a silicon epitaxial layer (to be abbreviated as “epitaxial layer” in some cases hereinafter) on a main surface of a silicon single-crystal substrate (to be abbreviated as “silicon substrate” in some cases hereinafter). An example of the vapor phase growth employs a hot-wall type vertical low pressure CVD apparatus. In this example, the inside of the reaction chamber (process chamber) is set to a relatively low temperature (for example, 600 to 1,000° C.) (as compared to the temperature condition of the mainstream, that is, about 1,100° C.) and a reduced pressure state. While maintaining this state, monosilane gas or dichlorosilane gas is supplied as a silicon material gas into the reaction chamber. In the chamber, a silicon epitaxial layer is grown by vapor phase growth (to be called as “low temperature epitaxial growth” in some cases hereinafter).
With use of the low temperature epitaxial growth method, which involves a low temperature process, the outer diffusion of dopant from the silicon substrate to the epitaxial layer, which is caused by heating, can be suppressed. Therefore, it is possible to obtain an appropriate steep change in resistivity (or change in dopant concentration) at a boundary between the substrate and epitaxial layer. Further, although the growth rate of the epitaxial layer is low (as compared to the case of high temperature), this method can carry out vapor phase growth on a number of (for example, about 25 to 100) silicon substrates mounted on a so-called boat all at once, thereby achieving a very high productivity.
However, the inventors of the present invention found that when a low-temperature epitaxial growth is carried out with use of a hot-wall type vertical low pressure CVD apparatus as described above, the haze level (the degree of surface roughness) of the grown epitaxial layer would be high.